Group I introns in the liverwort mitochondrial genome: The gene coding for subunit 1 of cytochrome oxidase shares five intron positions with its fungal counterparts

Abstract

The complete nudeotlde sequence of the mrtochondrial DNA (mtDNA) from a liverwort, Marchantla polymorpha, contains thirty-two introns. Twenty-five of these introns possess the characteristic secondary structures and consensus sequences of group II Introns. The remaining seven are group I Introns, six of which happen to interrupt the gene coding for subunlt 1 of cytochrome oxidase (cox1). Interestingly, the insertion sites of one group II and four group I introns in the cox1 gene coincide with those of the respective fungal mitochondrlal introns. Moreover, comparison of the four group I introns with their fungal counterparts shows that group I introns inserted at identical genomlc sites in different organisms are indeed related to one another, In terms of the peptlde sequences generated from the complete or fragmental ORFs encoded by these introns. At the same time, the liverwort introns turned out to be more divergent from their fungal cognates than the latter are from one another. We therefore conclude that vertical transmission from a common ancestor organism is the simplest explanation for the presence of cognate introns in liverwort and fungal mitochondrlal genomes. © 1993 Oxford University Press.